Flexible transmitter tensioner for outboard motor

ABSTRACT

An engine for an outboard motor includes an engine body, a crankshaft and one or more camshafts. A camshaft drive mechanism is arranged on a top surface of the engine body. The camshaft drive mechanism includes a timing belt to rotate the camshafts with the rotation of the crankshaft. A belt tensioner is arranged to adjust tension of the timing belt. The tensioner includes a shaft unit mounted on the engine body. A peripheral unit is swingably carried by the shaft unit and abutting on a portion of the timing belt. A swing axis of the shaft unit is offset from a center axis of the peripheral unit. The tensioner further includes a hydraulic damping mechanism to damp a vibration of the timing belt. The damping mechanism has a piston rod that urges the peripheral unit toward the timing belt. The piston rod is positioned at a location which can be generally the highest of the damping mechanism when a drive unit of the outboard motor is tilted up about a tilt axis. The shaft unit also is positioned at another location which can be higher than the center axis of the peripheral unit when the drive unit of the outboard motor is tilted up about the tilt axis.

PRIORITY INFORMATION

[0001] This application is based on and claims priority to JapanesePatent Application No. 2001-030696, filed Feb. 7, 2001, the entirecontents of which is hereby expressly incorporated by reference. Thisapplication further claims the benefit of U.S. Provisional ApplicationNo. 60/322,482 filed Sep. 13, 2001.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates generally to a flexible transmittertensioner for an outboard motor, and more particularly to an improvedflexible transmitter tensioner that has a swing axis disposed offsetfrom a center axis of the tensioner.

[0004] 2. Description of Related Art

[0005] Internal combustion engines that are used in outboard motorstypically comprise a crankshaft that drives a submerged marinepropulsion device through suitable shaft couplings. The crankshaft alsocan drive a variety of engine components, such as, for example, one ormore camshafts and accessories. The accessories can include alternatorsor generators, high-pressure fuel pumps and various other types ofdevices employed for the engine operation. Normally, a flexibletransmitter, such as a drive belt or chain, for example, that isdisposed atop the engine, drives these devices.

[0006] Many of these flexible transmitters, however, tend to elongateduring periods of long use. Moreover, distances between the variousshafts may increases or decreased during engine operation due totemperature-based expansion of the engine. A tensioner, thus, isnecessary to adjust tension of the flexible transmitter during operationof such engines. Without such a tensioner, the flexible transmitter mayeither slip or bind the driven camshafts and/or accessories. Suchslipping or binding is detrimental to engine performance because thecamshafts are required to rotate in a strict timed relationship with thecrankshaft.

[0007] Tensioners that automatically adjust the tension on the flexibletransmitter currently are provided for automobile engines. For example,Japanese Laid Open Publications No. H08-338488 and No. H10-122316disclose some exemplary constructions of such automatic tensioners. Thetensioners usually comprise a shaft unit and a peripheral unit thatabuts on a flexible transmitter. The shaft unit is offset from a centeraxis of the peripheral unit. A tension adjuster and a damping mechanismalso are provided. The tension adjuster adjusts tension of the flexibletransmitter and the damping mechanism reduces vibration of the flexibletransmitter. The damping mechanism normally comprises a hydrauliccylinder system that includes a piston rod extending beyond an end of acylinder. The cylinder system urges the peripheral unit of the tensionertoward the flexible transmitter.

[0008] Outboard motors can employ the automatic tensioners. However, aproblem arises with particular environmental conditions of the outboardmotors and arrangements thereof. Although a protective cowling typicallysurrounds the engine, the outboard motor generally is used in mannersthat increase the likelihood of water and/or mist contacting the engine,including its accessories and accessory drive mechanisms. The water cancontain salt if the outboard motor is used in the ocean. Because of suchenvironmental conditions, water can enter the tensioner or can adhere toa surface of the tensioner.

[0009] In addition, the outboard motor typically comprises a drive unitthat includes the engine and a bracket assembly that is mounted on anassociated watercraft and supports the drive unit for tilt movementabout a horizontally extending tilt axis. When the drive unit is tiltedup, the tensioner that is disposed atop of the engine slants and thewater that has entered or adhered to the tensioner tends to accumulateat a lower portion of the tensioner. The water can corrode members ofthe tensioner disposed at the lower portion if the drive unit is held inthe tilted up position for a long period. Additionally, salt can adhereto the members. Such corrosion or salt deposition is disadvantageousbecause either situation can cause the tensioner to malfunction, whichmight leave the engine operating as though no tensioner was provided atall.

SUMMARY OF THE INVENTION

[0010] Accordingly, a need exists for an improved flexible transmittertensioner for an outboard motor.

[0011] In accordance with one aspect of the present invention, anoutboard motor comprises a drive unit. A bracket assembly is adapted tobe mounted on an associated watercraft to support the drive unit fortilt movement about a horizontally extending tilt axis. The drive unitincludes an internal combustion engine. The engine comprises an enginebody. A moveable member is moveable relative to the engine body. A firstrotatable member is rotatable with the movement of the moveable member.An engine component actuation mechanism is arranged to actuate at leastone of engine components. The actuation mechanism includes a secondrotatable member arranged to engage the engine component. A drivemechanism is arranged on a top surface of the engine body to drive theactuation mechanism. The drive mechanism includes a flexible transmitterto rotate the second rotatable member with the rotation of the firstrotatable member. A tensioner is arranged to adjust tension of theflexible transmitter. The tensioner comprises a shaft unit mounted onthe engine body. A peripheral unit is swingably carried by the shaftunit and abutting on a portion of the flexible transmitter. A mount axisof the shaft unit is offset from a center axis of the peripheral unit. Adamping mechanism is provided to damp a vibration of the flexibletransmitter. The damping mechanism has a damping member that urges theperipheral unit toward the flexible transmitter. The damping member ispositioned at a location which is capable to be generally the highest ofthe damping mechanism when the drive unit is tilted up about the tiltaxis.

[0012] In accordance with another aspect of the present invention, anoutboard motor comprises a drive unit. A bracket assembly is adapted tobe mounted on an associated watercraft to support the drive unit fortilt movement about a horizontally extending tilt axis. The drive unitincludes an internal combustion engine. The engine comprises an enginebody. A moveable member is moveable relative to the engine body. Theengine body and the moveable member together define at least onecombustion chamber. A first rotatable member is rotatable with themovement of the moveable member. An air intake system is arranged tointroduce air to the combustion chamber. The intake system includes atleast one intake valve. An exhaust system is arranged to route exhaustgases from the combustion chamber. The exhaust system includes at leastone exhaust valve. A valve actuation mechanism is arranged to actuate atleast one of the intake and exhaust valves between an open position anda closed position. The valve actuation mechanism includes a secondrotatable member arranged to engage the at least one of the intake andexhaust valves. A drive mechanism is arranged on a top surface of theengine body to drive the valve actuation mechanism. The drive mechanismincludes a flexible transmitter to rotate the second rotatable memberwith the rotation of the first rotatable member. A tensioner is arrangedto adjust tension of the flexible transmitter. The tensioner comprises ashaft unit mounted on the engine body. A peripheral unit is swingablycarried by the shaft unit and abutting on a portion of the flexibletransmitter. A swing axis of the shaft unit is offset from a center axisof the peripheral unit. A damping mechanism is provided to damp avibration of the flexible transmitter. The damping mechanism has adamping member that urges the peripheral unit toward the flexibletransmitter. The damping member is positioned at a location which iscapable to be generally the highest of the damping mechanism when thedrive unit is tilted up about the tilt axis.

[0013] In accordance with a further aspect of the present invention, anoutboard motor comprises a drive unit. A bracket assembly is adapted tobe mounted on an associated watercraft to support the drive unit fortilt movement about a horizontally extending tilt axis. The drive unitincludes an internal combustion engine. The engine comprises an enginebody. A moveable member is moveable relative to the engine body. A firstrotatable member is rotatable with the movement of the moveable member.An engine component actuation mechanism is arranged to actuate at leastone of engine components. The actuation mechanism includes a secondrotatable member arranged to engage the engine component. A drivemechanism is arranged on a top surface of the engine body to drive theactuation mechanism. The drive mechanism includes a flexible transmitterto rotate the second rotatable member with the rotation of the firstrotatable member. A tensioner is arranged to adjust tension of theflexible transmitter. The tensioner comprises a shaft unit mounted onthe engine body. A peripheral unit is swingably carried by the shaftunit and abutting on a portion of the flexible transmitter. A swing axisof the shaft unit is offset from a center axis of the peripheral unit.The shaft unit is positioned at a location which is capable to begenerally positioned higher than the center axis of the peripheral unitwhen the drive unit is tilted up about the tilt axis.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] These and other features, aspects and advantages of the presentinvention will now be described with reference to the drawings of apreferred embodiment, which embodiment is intended to illustrate and notto limit the present invention. The drawings comprise four figures.

[0015]FIG. 1 is a side elevational view of an outboard motor configuredin accordance with certain features, aspects and advantages of thepresent invention. An associated watercraft is partially shown insection.

[0016]FIG. 2 is an enlarged side elevational view of an engine of theoutboard motor. A protective cowling is shown in phantom line.

[0017]FIG. 3 is a top plan view of the engine of FIG. 2. An engine coverand a flywheel magneto are shown in phantom line.

[0018]FIG. 4 is a partial top plan view of the engine of FIG. 2illustrating a timing belt tensioner that is arranged and configured inaccordance with certain features, aspects and advantages of the presentinvention.

DETAILED DESCRIPTION OF ONE PREFERRED EMBODIMENT OF THE PRESENTINVENTION

[0019] With reference to FIGS. 1-3, an overall construction of anoutboard motor 30 that features an improved timing belt tensioner 32,which is arranged and configured in accordance with certain features,aspects and advantages of the present invention, will be described.

[0020] In the illustrated arrangement, the outboard motor 30 generallycomprises a drive unit 34 and a bracket assembly 36. The bracketassembly 36 supports the drive unit 34 on a transom 38 of an associatedwatercraft 40 and places a marine propulsion device in a submergedposition with the watercraft 40 resting relative to a surface of a bodyof water. The bracket assembly 36 preferably comprises a swivel bracket44, a clamping bracket 46, a steering shaft and a pivot pin 50.

[0021] The steering shaft typically extends through the swivel bracket44 and is affixed to the drive unit 34. The steering shaft can bepivotally journaled for steering movement about a generally verticallyextending steering axis defined within the swivel bracket 44. Theclamping bracket 46 comprises a pair of bracket arms that preferably arelaterally spaced apart from each other and that are attached to thewatercraft transom 38.

[0022] The pivot pin 50 completes a hinge coupling between the swivelbracket 44 and the clamping bracket 46. The pivot pin 50 preferablyextends through the bracket arms so that the clamping bracket 46supports the swivel bracket 44 for pivotal movement about a generallyhorizontally extending tilt axis defined by the pivot pin 50. The driveunit 34 thus can be tilted or trimmed about the pivot pin 50.

[0023] As used through this description, the terms “forward,”“forwardly” and “front” mean at or to the side where the bracketassembly 36 is located, unless indicated otherwise or otherwise readilyapparent from the context use. The terms “rear,” “reverse,” “backwardly”and “rearwardly” mean at or to the opposite side of the front side.

[0024] A hydraulic tilt and trim adjustment system preferably isprovided between the swivel bracket 44 and the clamping bracket 46 fortilt movement (raising or lowering) of the swivel bracket 44 and thedrive unit 34 relative to the clamping bracket 46. In some arrangements,the outboard motor 30 can have a manually operated system for tiltingthe drive unit 34. Typically, the term “tilt movement,” when used in abroad sense, comprises both a tilt movement and a trim adjustmentmovement.

[0025] The illustrated drive unit 34 comprises a power head 58 and ahousing unit 60, which includes a driveshaft housing 62 and a lower unit64. The power head 58 is disposed atop the housing unit 60 and includesan internal combustion engine 65 that is positioned within a protectivecowling assembly 66, which preferably is made of plastic. In mostarrangements, the protective cowling assembly 66 defines a generallyclosed cavity 68 in which the engine 65 is disposed. The engine, thus,is generally protected within the enclosure, which is defined by thecowling assembly 66, from environmental elements.

[0026] The protective cowling assembly 66 preferably comprises a topcowling member 70 and a bottom cowling member 72. The top cowling member70 preferably is detachably affixed to the bottom cowling member 72 by acoupling mechanism to facilitate access to the engine and other relatedcomponents.

[0027] The top cowling member 70 preferably has a rear intake opening(not shown) defined through an upper rear portion. A rear intake memberwith one or more air ducts can be unitarily formed with, or affixed to,the top cowling member 70. The rear intake member, together with theupper rear portion of the top cowling member 70, generally defines arear air intake space. Ambient air is drawn into the closed cavity 68via the rear intake opening and the air ducts of the rear intake member.Typically, the top cowling member 70 tapers in girth toward its topsurface, which is in the general proximity of the air intake opening.The taper helps to reduce the lateral dimension of the outboard motor,which helps to reduce the air drag on the watercraft 40 during movement.

[0028] The bottom cowling member 72 preferably has an opening throughwhich an upper portion of an exhaust guide member 80 extends. Theexhaust guide member 80 preferably is made of aluminum alloy and isaffixed atop the driveshaft housing 62. The bottom cowling member 72 andthe exhaust guide member 80 together generally form a tray. The engine65 is placed onto this tray and can be connected to the exhaust guidemember 80. The exhaust guide member 80 also defines an exhaust dischargepassage through which burnt charges (e.g., exhaust gases) from theengine 65 pass.

[0029] The engine 65 in the illustrated embodiment preferably operateson a four-cycle combustion principle. With reference now to FIGS. 2 and3, the presently preferred engine 65 is a DOHC six cylinder engine andhas a V-shaped cylinder block 84. The cylinder block 84 thus defines twocylinder banks which extend generally side by side with each other. Inthe illustrated arrangement, each cylinder bank has three cylinder boressuch that the cylinder block 84 has six cylinder bores in total. Thecylinder bores of each bank extend generally horizontally and aregenerally vertically spaced from one another. This type of engine,however, merely exemplifies one type of engine. Engines having othernumbers of cylinders, having other cylinder arrangements (in-line,opposing, etc.), and operating on other combustion principles (e.g.,crankcase compression two-stroke or rotary) also can be used. Theillustrated engine 65 generally is symmetrical about a longitudinalcenter plane 88 (FIG. 3) that extends generally vertically and fore toaft of the outboard motor 30.

[0030] As used in this description, the term “horizontally” means thatthe subject portions, members or components extend generally in parallelto the water surface (i.e., generally normal to the direction ofgravity) when the associated watercraft 40 is substantially stationarywith respect to the water surface and when the drive unit 34 is nottilted (i.e., is placed in the position shown in FIG. 1). The term“vertically” in turn means that portions, members or components extendgenerally normal to those that extend horizontally.

[0031] A moveable member, such as a reciprocating piston, moves relativeto the cylinder block 84 in a suitable manner. In the illustratedarrangement, a piston (not shown) reciprocates within each cylinderbore. Because the cylinder block 84 is split into the two cylinderbanks, each cylinder bank extends outward at an angle to an independentfirst end in the illustrated arrangement. A pair of cylinder headmembers 92 are affixed to the respective first ends of the cylinderbanks to close those ends of the cylinder bores. The cylinder headmembers 92 together with the associated pistons and cylinder bores,preferably define six combustion chambers (not shown). Of course, thenumber of combustion chambers can vary, as indicated above. Each of thecylinder head member 92 is covered with a cylinder head cover member 94.

[0032] A crankcase member 96 is coupled with the cylinder block 84 and acrankcase cover member 98 is further coupled with the crankcase member96. The crankcase member 96 and the crankcase cover member 98 close theother end of the cylinder bores and, together with the cylinder block84, define a crankcase chamber. A first rotatable member, such as acrankshaft 100, extends generally vertically through the crankcasechamber and can be journaled for rotation about a rotational axis byseveral bearing blocks. The rotational axis of the crankshaft 100preferably is on the longitudinal center plane 88. Connecting rodscouple the crankshaft 100 with the respective pistons in any suitablemanner. Thus, the reciprocal movement of the pistons rotates thecrankshaft 100.

[0033] Preferably, the crankcase cover member 98 is located at theforward-most position of the engine 65, with the crankcase member 96,the cylinder block 84, the cylinder head members 92 and the cylinderhead cover members 94 being disposed rearward from the crankcase covermember 98, one after another. In the illustrated arrangement, thecylinder block 84, the cylinder head members 92, the cylinder head covermembers 94, the crankcase member 96 and the crankcase cover member 98together define an engine body 102. Preferably, at least these majorengine portions 84, 92, 94, 96, 98 are made of aluminum alloy. In somearrangements, the cylinder head cover members 94 can be unitarily formedwith the respective cylinder head members 92. Also, the crankcase covermember 98 can be unitarily formed with the crankcase member 96.

[0034] The engine 65 also comprises an air intake system 106. The airintake system 106 draws air from within the cavity 68 to the combustionchambers. The air intake system 106 preferably comprises six intakepassages 108 and a pair of plenum chambers 110. In the illustratedarrangement, each cylinder bank communicates with three intake passages108 and one plenum chamber 110.

[0035] The most-downstream portions of the intake passages 108 aredefined within the cylinder head members 92 as inner intake passages.The inner intake passages communicate with the combustion chambersthrough intake ports, which are formed at inner surfaces of the cylinderhead members 92. Typically, each of the combustion chambers has one ormore intake ports. Intake valves are slideably disposed at each cylinderhead members 92 to move between an open position and a closed position.As such, the valves act to open and close the ports to control the flowof air into the combustion chamber. Biasing members, such as springs,are used to urge the intake valves toward the respective closedpositions by acting between a mounting boss formed on each cylinder headmember 92 and a corresponding retainer that is affixed to each of thevalves. When each intake valve is in the open position, the inner intakepassage that is associated with the intake port communicates with theassociated combustion chamber.

[0036] Outer portions of the intake passages 108, which are disposedoutside of the cylinder head members 92, preferably are defined withintake conduits 114. In the illustrated arrangement, each intake conduit114 is formed with two pieces. One piece is a throttle body 116 in whicha throttle valve assembly 118 is positioned. The throttle valveassemblies 118 are schematically illustrated in FIG. 2. The throttlebodies 116 are connected to the inner intake passages. Another piece isan intake runner 120 disposed upstream of the throttle body 116. Therespective intake conduits 114 extend forwardly along side surfaces ofthe engine body 102 on both the port side and the starboard side fromthe respective cylinder head members 92 to the front of the crankcasecover member 98. The intake conduits 114 on the same side extendgenerally in parallel to each other and are vertically spaced apart fromone another.

[0037] Each throttle valve assembly 118 preferably includes a throttlevalve. Preferably, the throttle valves are butterfly valves that havevalve shafts journaled for pivotal movement about a generally verticalaxis. In some arrangements, the valve shafts are linked together and areconnected to a control linkage. The control linkage would be connectedto an operational member, such as a throttle lever, that is provided onthe watercraft or otherwise proximate the operator of the watercraft 40.The operator can control the opening degree of the throttle valves inaccordance with operator demand through the control linkage. That is,the throttle valve assemblies 118 can measure or regulate amounts of airthat flow through the intake passages 108 to the combustion chambers inresponse to the operation of the operational member by the operator.Normally, the greater the opening degree, the higher the rate of airflowand the higher the engine speed.

[0038] The respective plenum chambers 110 preferably are defined withplenum chamber units 124 which are disposed side by side in front of thecrankcase cover member 98 and are affixed thereto. Preferably, theplenum chamber units 124 are arranged substantially symmetricallyrelative to the longitudinal center plane 88. In the illustratedarrangement, each forward end portion of the intake runners 120 ishoused within each plenum chamber unit 124. As shown in FIG. 2, eachplenum chamber unit 124 preferably has two air inlets 126, which extendgenerally rearwardly between the respective intake runners 120. Therespective air inlets 126 define inlet openings 128 through which air isdrawn into the plenum chambers 110. The intake runners 120 and the airinlets 126 can be unitarily formed with the associated plenum chamberunit 124 and those three components 120, 124, 126 can be made ofplastic. The respective plenum chamber units 124 are connected with eachother through one or more connecting pipes 130 (FIG. 3) to substantiallyequalize the internal pressures within each chamber unit 124. The plenumchambers 110 coordinate or smooth air delivered to each intake passage108 and also act as silencers to reduce intake noise.

[0039] The air within the closed cavity 68 is drawn into the plenumchambers 110 through the inlet openings 128 of the air inlets 126. Theair expands within the plenum chambers 110 to reduce pulsations and thenenters the outer intake passages 108. The air passes through the outerintake passages 108 and flows into the inner intake passages. The levelof airflow is measured by the throttle valve assemblies 118 before theair enters the inner intake passages.

[0040] The engine 65 further comprises an exhaust system that routesburnt charges, i.e., exhaust gases, to a location outside of theoutboard motor 30. Each cylinder head member 92 defines a set of innerexhaust passages that communicate with the combustion chambers throughone or more exhaust ports, which may be defined at the inner surfaces ofthe respective cylinder head members 92. The exhaust ports can beselectively opened and closed by exhaust valves. The construction ofeach exhaust valve and the arrangement of the exhaust valves aresubstantially the same as the intake valve and the arrangement thereof,respectively. Thus, further description of these components is deemedunnecessary.

[0041] Exhaust manifolds preferably are defined generally verticallywithin the cylinder block 84 between the cylinder bores of both thecylinder banks. The exhaust manifolds communicate with the combustionchambers through the inner exhaust passages and the exhaust ports tocollect exhaust gases therefrom. The exhaust manifolds are coupled withthe exhaust discharge passage of the exhaust guide member 80. When theexhaust ports are opened, the combustion chambers communicate with theexhaust discharge passage through the exhaust manifolds.

[0042] A valve cam mechanism preferably is provided for actuating theintake and exhaust valves in each cylinder bank. Preferably, the valvecam mechanism includes second rotatable members such as a pair ofcamshafts 132 per cylinder bank, although one of them is not seen in theillustrated arrangement. The camshafts 132 preferably comprise intakeand exhaust camshafts. The camshafts 132 preferably extend generallyvertically and are journaled for rotation between the cylinder headmembers 92 and the cylinder head cover members 94. The camshafts 132have cam lobes to push valve lifters that are affixed to the respectiveends of the intake and exhaust valves in any suitable manner. The camlobes repeatedly push the valve lifters in a timed manner, which is inproportion to the engine speed. The movement of the lifters generally istimed by rotation of the camshafts 132 to appropriately actuate theintake and exhaust valves.

[0043] A camshaft drive mechanism 134 preferably is provided for drivingthe valve cam mechanism. The camshaft drive mechanism 134 in theillustrated arrangement is formed above a top surface 135 (see FIG. 2)of the engine body 102 and comprises driven sprockets 136 positionedatop at least one of each pair of camshafts 132, a drive sprocket 138positioned atop the crankshaft 100 and a flexible transmitter, such as atiming belt or chain 140, for instance, wound around the drivensprockets 136 and the drive sprocket 138. The crankshaft 100 thus drivesthe respective camshafts 132 through the timing belt 140 in the timedrelationship.

[0044] The illustrated timing belt 140 moves in a direction indicated bythe arrows 141 shown in FIG. 3. The belt tensioner 32 advantageouslymaintains the timing belt 140 under a desired degree of tension. Thebelt tensioner 32 preferably is mounted on the cylinder block 84 so thata peripheral unit 142 of the belt tensioner 32 abuts on a portion of thetiming belt 140. In the illustrated arrangement, the other camshaft (notshown) on each bank is driven by the first camshaft via another timingbelt or chain (not shown). Because the camshafts 132 must rotate at halfof the speed of the rotation of the crankshaft 100 in a four-cycleengine, a diameter of the illustrated driven sprockets 136 is twice aslarge as a diameter of the illustrated drive sprocket 138. The camshaftdrive mechanism 134, including the belt tensioner 142, will be describedin greater detail later.

[0045] Most of the engine components described above are well known tothose skilled in the art and are disclosed, for example, in U.S. PatNos. 5,704,819, 5,865,655, 5,941,205 and 6,044,817, the disclosures ofwhich are hereby incorporated by reference in their entirety.

[0046] The illustrated engine 65 further comprises indirect, port orintake passage fuel injection. In one arrangement, the engine 65comprises direct fuel injection and, in another arrangement, the engine65 is carbureted. The illustrated fuel injection system preferablycomprises six fuel injectors 144 with one fuel injector allotted to eachone of the respective combustion chambers. The fuel injectors 144preferably are mounted on the throttle bodies 116 of the respectivebanks with a pair of fuel rails 146. In the illustrated arrangement, thefuel rails 146 connect the fuel injectors 144 on the same banks witheach other and also define portions of fuel conduits to deliver fuel tothe injectors 144.

[0047] Each fuel injector 144 preferably has an injection nozzledirected downstream within the associated intake passage 108. Theinjection nozzle preferably is disposed downstream of the throttle valveassembly 118. The fuel injectors 144 spray fuel into the intake passages108 under control of an electronic control unit (ECU) (not shown). TheECU controls both the initiation timing and the duration of the fuelinjection cycle of the fuel injectors 144 so that the nozzles spray adesired amount of fuel each combustion cycle.

[0048] A fuel supply tank preferably is disposed on a hull of theassociated watercraft 40. The fuel supply tank contains a supply offuel. From the tank, the fuel is delivered to the fuel rails 146 throughsuitable fuel conduits.

[0049] A vapor separator 148 preferably is in fluid communication withthe tank and the fuel rails, and can be disposed along the conduits inone arrangement. The vapor separator 148 separates vapor from the fueland can be mounted on the engine body 102 at the side surface on theport side.

[0050] The fuel injection system preferably employs at least two fuelpumps to deliver the fuel to the vapor separator 148 and to send out thefuel therefrom. More specifically, in the illustrated arrangement, alower pressure pump 150, which is affixed to the vapor separator 148,pressurizes the fuel toward the vapor separator 148 and a high pressurepump (not shown), which is disposed within the vapor separator 148,pressurizes the fuel passing out of the vapor separator 148.

[0051] A vapor delivery conduit 152 couples the vapor separator 148 withat least one of the plenum chambers 110. The vapor removed from the fuelsupply by the vapor separator 148 thus can be delivered to the plenumchamber 110 for delivery to the combustion chambers with the combustionair. In other applications, the engine 65 can be provided with aventilation system arranged to send lubricant vapor to the plenumchamber(s). In such applications, the fuel vapor also can be sent to theplenum chambers via the ventilation system.

[0052] The engine 65 further comprises an ignition system. Eachcombustion chamber is provided with a spark plug which preferably isdisposed between the intake and exhaust valves. Each spark plug haselectrodes that are exposed in the associated combustion chamber. Theelectrodes are spaced apart from each other by a small gap. The sparkplugs are connected to the ECU through ignition coils. The spark plugsgenerate a spark between the electrodes to ignite an air/fuel charge inthe combustion chamber according to desired ignition timing maps orother forms of controls.

[0053] Generally, during an intake stroke, air is drawn into thecombustion chambers through the air intake passages 108 and fuel ismixed with the air by the fuel injectors 144. The mixed air/fuel chargeis introduced to the combustion chambers. The mixture is then compressedduring a compression stroke. Just prior to a power stroke, therespective spark plugs ignite the compressed air/fuel charge in therespective combustion chambers. The air/fuel charge thus rapidly bumsduring the power stroke to move the pistons. The burnt charge, i.e.,exhaust gases, then is discharged from the combustion chambers during anexhaust stroke.

[0054] A flywheel assembly 156, which is schematically illustrated withphantom line in FIG. 3, preferably is positioned atop the crankshaft 100and is mounted for rotation with the crankshaft 100. The flywheelassembly 156 comprises a flywheel magneto or AC generator that supplieselectric power directly or indirectly via a battery to variouselectrical components such as the fuel injection system, the ignitionsystem and the ECU. An engine cover 158 preferably extends over almostall of the engine 65, including the flywheel assembly 156.

[0055] The engine 65 may comprise any other systems, mechanisms,devices, accessories and components other than those described abovesuch as, for example, a cooling system and a lubrication mechanism.Those systems, mechanisms, devices, accessories and components can bedirectly or indirectly driven by the crankshaft 100 through a flexibletransmitter, such as the timing belt 140. In some arrangements, flexibletransmitter tension can be adjusted by two or more tensioners that arearranged and configured in accordance with certain features, aspects andadvantages of the present invention.

[0056] With reference again to FIG. 1, the driveshaft housing 62 dependsfrom the power head 58 and supports a driveshaft, which is coupled withthe crankshaft 100 and which extends generally vertically through thedriveshaft housing 62. The driveshaft is journaled for rotation and isdriven by the crankshaft 100.

[0057] The driveshaft housing 62 preferably defines an internal sectionof the exhaust system that leads the majority of exhaust gases to thelower unit 64. The internal section includes an idle discharge portionthat extends from a main portion of the internal section to dischargeidle exhaust gases directly to the atmosphere through a discharge portthat is formed on a rear surface of the driveshaft housing 62 engineidle.

[0058] The lower unit 64 depends from the driveshaft housing 62 andsupports a propulsion shaft that is driven by the driveshaft. Thepropulsion shaft extends generally horizontally through the lower unit64 and is journaled for rotation. A propulsion device is attached to thepropulsion shaft. In the illustrated arrangement, the propulsion deviceis a propeller 160 that is affixed to an outer end of the propulsionshaft. The propulsion device, however, can take the form of a dualcounter-rotating system, a hydrodynamic jet, or any of a number of othersuitable propulsion devices.

[0059] A transmission preferably is provided between the driveshaft andthe propulsion shaft, which lie generally normal to each other (i.e., ata 90° shaft angle) to couple together the two shafts by bevel gears. Theoutboard motor 30 has a clutch mechanism that allows the transmission tochange the rotational direction of the propeller 160 among forward,neutral or reverse.

[0060] The lower unit 64 also defines an internal section of the exhaustsystem that is connected with the internal exhaust section of thedriveshaft housing 62. At engine speeds above idle, the exhaust gasesgenerally are discharged to the body of water surrounding the outboardmotor 30 through the internal sections and then a discharge sectiondefined within the hub of the propeller 160.

[0061] With reference still to FIG. 3 and with additional reference toFIG. 4, the illustrated camshaft drive mechanism 134 and the illustratedtiming belt tensioner 32 will now be described in great detail. Thetiming belt tensioner 32 preferably comprises the peripheral unit 142, ashaft unit 170, an offset member 174, a tension adjuster 176 and adamping mechanism 178.

[0062] The shaft unit 170 comprises a shaft affixed to the top surface135 of the engine body 102 and, more specifically, to the cylinder block84 in the illustrated arrangement. In the illustrated arrangement, ahexagonal socket-head bolt 180 is the shaft and also functions to securethe shaft unit 170 to the cylinder block 84. The bolt 180 has a headportion 182 which has an outer diameter that is greater than an outerdiameter of a shaft portion. A hexagon recess 184 is formed at the headportion 182 to fasten or loosen the bolt 180 with a hexagon head tool(e.g., an Allen wrench) that has a proper outer diameter fitting with aninner diameter of the hexagon recess 184. The shaft unit 170 preferablyincludes a collar 186 surrounding the shaft portion. The balance of theillustrated tensioner 32, which includes the peripheral unit 142 and theoffset member 174, is pivotally supported by the shaft 180 via thecollar 186.

[0063] The illustrated peripheral unit 142 comprises a tension pulley190 and a bearing assembly 192 that journals the tension pulley 190. Thetension pulley 190 abuts a portion of the timing belt 140. Theillustrated tension pulley 190 abuts on the belt 140 in a range 194 asshown in FIG. 4. More than one tension pulley 190 can be used and thelocation of the tension pulley 190 can be varied to accommodate variousengine components.

[0064] The bearing assembly 192 includes an inner ring 196, a pluralityof rollers or balls and retainers. A combination of the rollers (orballs) and the retainers are schematically indicated by a referencenumeral 198. Generally speaking, the peripheral unit 142 defines aroller bearing or a ball bearing. In other words, the tension pulley 190and the inner ring 196 define an outer race and an inner race of thebearing, respectively, with the rollers (or balls) being positionedbetween the two components. Thus, the tension pulley 190 is rotatablerelative to the inner ring 196. Alternatively, the peripheral unit 172can be further provided with an outer ring or race that is independentof the pulley 190.

[0065] The illustrated tension pulley 190 has a height taller than aheight of the bearing assembly 192. Both the tension pulley 190 and thebearing assembly 192 preferably are generally made of metal material. Anouter surface of the tension pulley 190 that contacts the timing belt140 preferably is coated with a non-electrolytic nickel plating. Becauseof this plating, a relatively deep and hard plating layer is formed andthe outer surface of the tension pulley 190 is well protected from watercorrosion even if salt is contained in the water.

[0066] The offset member 174 couples the peripheral unit 142 with theshaft unit 170 such that respective rotational axes of each is offsetfrom the other. More specifically, a swing axis 200 of the shaft unit170 is offset from a center axis 202 of the peripheral unit 142 as shownin FIG. 4.

[0067] The illustrated offset member 174 substantially occupies a spacesurrounded by the peripheral unit 142 except the shaft unit 170. Theoffset member 174 is positioned above the damping mechanism 178.Desirably, the shaft unit 170 is positioned at a location which ispositioned generally higher than the center axis 202 when the drive unit34 is tilted up about the tilt axis defined the pivot pin 50.

[0068] An engagement portion, such as a pin 204, preferably extendsdownwardly from a bottom surface of the offset member 174. In otherwords, an axis 206 of the engage portion, i.e., the pin 204 extendsgenerally vertically. The pin 204 preferably is positioned next to theshaft unit 170. In one arrangement, the pin 204 is a discrete membermounted to the offset member 174 and, in another arrangement, the pin204 is a projection integrally formed on the offset member 174.

[0069] The offset member 174 preferably is made of metal alloymanufactured by a sintering process. A top surface of the offset member174 preferably is treated with a Parkerizing process that gives ananti-corrosion property to the top surface.

[0070] The offset member 174 comprises an elongated recess 208 that hasa longitudinal axis 210 that extends generally horizontally. The axis210 preferably extends toward a contact position 211 where the belt 194contacts the tension pulley 190.

[0071] The recess 208 receives the tension adjuster 176, which comprisesa bias member, such as a spring 212, a spring retainer 214 and a pin216. The pin 216 extends upwardly from the damping mechanism 178. In theillustrated arrangement, an axis 218 of the pin 216 extends generallyvertically.

[0072] The bias spring 212 preferably is a coil spring and is confinedwithin the recess 208 along the axis 210 under a compressed conditionbetween one end 219 of the recess 208 and a spring retainer 214, whichis secured in position between the spring 212 and the pin 216. Thespring 212 thus pushes the offset member 174 against the pin 216, whichsets up forces that bias the peripheral unit 142 toward the timing belt140. The biasing force of the spring 212 swings the tensioner 32 aroundthe swing axis 200 of the shaft unit 170. The tensioner 32 swings untila tension force of the timing belt 140 and the biasing force of thespring 212 balance. Accordingly, the tension of the timing belt 140 iswell adjusted.

[0073] The damping mechanism 178 reduces vibration of the timing belt140. In the illustrated arrangement, the mechanism 178 is placedgenerally below the offset member 174 and the peripheral unit 142, andcomprises a hydraulic cylinder member 220 that defines a cavity 222. Thecavity 222 comprises a longitudinally extending damping axis 224 thatextends generally horizontally. The axis 224 preferably is orientedtoward a portion 226 of the pulley 190 where the belt 194 is separatingfrom the tension pulley 190. The axis 206 of the pin 204 preferablyintersects with this axis 224 and the axis 206 of the pin 204 preferablylies generally normal to the axis 224.

[0074] An end portion 225 of the cylinder member 220 extends out of theperipheral unit 142 and is affixed to the cylinder block 84 by afastener, such as a bolt 226, for instance, which comprises a verticalaxis 227. The cylinder member 220 comprises a projecting portion thatextends toward the shaft unit 170. This projecting portion also can beaffixed to the cylinder block 84, together with the shaft unit 170, bythe hex socket head bolt 180, for instance. The pin 216 extends upwardlyfrom the projecting portion of the cylinder member 220. In onearrangement, the pin 216 is a discrete member mounted to the cylindermember 220 and, in another arrangement, the pin 216 is a projectionformed on the cylinder member 220.

[0075] In the illustrated arrangement, a hydraulic piston 228 isslideably disposed within the cavity 222 along the axis 224 and definesfirst and second chambers 230, 232 on opposite sides thereof. An orifice236 formed through the piston 228 generally in parallel to the axis 224connects both the first and second chambers 230, 232. A damping member,such as a piston rod 238, for instance, that is coupled with the piston228 extends through the first chamber 230 and beyond the end of thecylinder member 220 that is located next to the pin 204. The term“coupled with” means either that the piston rod 238 is a separate memberfrom the piston 228 and then is affixed to the piston 228 or that thepiston rod 238 is unitarily formed with the piston 228. Desirably, thepiston rod 238 is positioned at a location that is generally the highestportion of the damping mechanism 178 when the drive unit 34 is tilted upabout the tilt axis defined by the pivot pin 50. Nevertheless, the pin204 preferably is positioned higher than the piston rod 238 under thetilt up condition.

[0076] The first and second chambers 230, 232 preferably are filled witha working fluid such as, for example, oil. The working fluid can movebetween the first and second chambers 230, 232 through the orifice 236when the piston 228 translates within the cavity 222. Preferably, theorifice 236 is narrow enough to generate some flow resistance when thefluid moves between the chambers 230, 232. Thus, movement of the piston228 is advantageously quite slow. Because a certain volume of the pistonrod 238 goes in and out of the cavity 222 with movement of the piston228, a fluid reservoir (not shown) can be provided in the dampingmechanism 178 to compensate for the volume of the piston rod 238.

[0077] In the illustrated arrangement, a bias spring 242 also isdisposed within the second chamber 232 to bias the piston 228 toward thepin 204. The bias spring 242 preferably is a compressed coil spring and,in one arrangement, is confined in the second chamber 232 (i.e., alongthe axis 224). Thus, the bias spring 242 normally pushes the piston rod238 toward the pin 204. Because the offset member 174, which comprisesthe pin 204, is coupled with the peripheral unit 142, the biasing forceof the spring 242 also biases the peripheral unit 142 toward the timingbelt 140.

[0078] Vibration of the belt 140 causes slight swings of the tensioner32 about the swing axis 200. With this slight swing, the pin 204 pushesthe piston rod 238 toward the bolt 227 or moves toward the timing belt140. However, the working fluid in the chambers 230, 232 inhibits thepiston 228 from moving quickly due to the narrow orifice 236.Accordingly, the pin 204 remains substantially at an initial positionand vibration is effectively damped.

[0079] As will be appreciated, the tensioner 32 for the outboard motor30 moves up and down with tilting movement of the drive unit 34. At anyposition between a fully tilted up position and a fully tilted downposition, the tensioner moves in accordance with the movement of theengine body 102. Accordingly, the tensioner 32 may be angled relative togravity and water adhering on the tensioner 32 can accumulate at a lowerportion of the tensioner 32 when the drive unit 34 is held in the tiltedup position for long time. To reduce the likelihood of such a situation,both the shaft unit 170 and the piston rod 238 are positioned above theportion of the outboard motor in which water typically accumulates.

[0080] Additionally, because the tension pulley 190 is moved with arelatively great force by the timing belt 140, insignificant corrosionor salt adhesion on the peripheral unit 142 itself does not matterseriously. In fact, the amount of force required to move the tensionpulley in the illustrated arrangement is several times greater than thatrequired to move prior tensioner arrangements. Moreover, because thepiston rod 238 is directed toward the separating portion 226 rather thanthe contact portion 211, water splash or water mist deflected by thetiming belt 140, if any, is unlikely to affect the piston rod 238.

[0081] Of course, the foregoing description is that of a preferredconstruction having certain features, aspects and advantages inaccordance with the present invention. Various changes and modificationsmay be made to the above-described arrangements without departing fromthe spirit and scope of the invention, as defined by the appendedclaims. For instance, the second rotatable member can be any one of anumber of engine components or accessories, other than the camshaftssuch as, for example, a fuel pump or an alternator inasmuch as thosecomponents are driven by a drive mechanism arranged on a top surface ofthe engine body. Accordingly, the scope of the present invention shouldnot be limited to the illustrated configurations, but should only belimited to a fair construction of the claims that follow and anyequivalents of the claims.

What is claimed is:
 1. An outboard motor comprising a drive unit, abracket assembly adapted to be mounted on an associated watercraft tosupport the drive unit for tilt movement about a horizontally extendingtilt axis, the drive unit comprising an internal combustion enginecomprising an engine body, a moveable member moveable relative to theengine body, a first rotatable member rotatable with the movement of themoveable member, an engine component comprising a second rotatablemember, and a drive mechanism arranged on a top surface of the enginebody, the drive mechanism comprising a flexible transmitter to rotatethe second rotatable member with the rotation of the first rotatablemember, a tensioner comprising a shaft unit mounted on the engine body,a peripheral unit pivotally supported by the shaft unit, the peripheralunit abutting on a portion of the flexible transmitter, said shaft unitdefining a mount axis and said peripheral unit defining a center axis,said mount axis and said center axis being offset, a damping mechanismconnected to the peripheral unit and comprising a damping member, thedamping member being positioned at a location which is generallyvertically higher than a balance of the damping mechanism when the driveunit is tilted up about the tilt axis.
 2. The outboard motor as setforth in claim 1, wherein the damping mechanism additionally comprises ahydraulic cylinder, the cylinder defining an internal cavity, a pistonslideably disposed within the internal cavity, the piston substantiallyseparating a first chamber and a second chamber that are defined withinthe internal cavity, the first and second chambers being filled withworking fluid, the piston comprising an orifice through which the firstand second chambers communicate with each other, and a bias member beingdisposed in the second chamber to bias the piston such that the dampingmechanism is extended.
 3. The outboard motor as set forth in claim 2,wherein at least a portion of the cylinder is mounted on the enginebody.
 4. The outboard motor as set forth in claim 2, wherein at least aportion of the cylinder is mounted on a portion of the shaft unit. 5.The outboard motor as set forth in claim 1, wherein the tensioneradditionally comprises an offset member coupled with the shaft unit, theoffset member comprising an engage portion and the damping mechanismengaging the engage portion.
 6. The outboard motor as set forth in claim5, wherein the engage portion is placed at a second location which iscapable of being generally positioned vertically higher than a shaftthat is connected to the piston of the damping mechanism when the driveunit is tilted up about the tilt axis.
 7. The outboard motor as setforth in claim 5, wherein the engage portion includes a pin extendingoutward from a balance of the offset member.
 8. The outboard motor asset forth in claim 1, wherein the tensioner additionally comprises anoffset member coupled with the shaft unit and the offset membergenerally covers the damping mechanism.
 9. The outboard motor as setforth in claim 8, wherein the offset member is made of a sinteredmaterial.
 10. The outboard motor as set forth in claim 9, wherein a topsurface of the offset member is treated with a Parkerizing process. 11.The outboard motor as set forth in claim 1, wherein the peripheral unithas an outer surface coated with a non-electrolytic metal plating. 12.The outboard motor as set forth in claim 11, wherein thenon-electrolytic metal plate includes a non-electrolytic nickel plating.13. The outboard motor as set forth in claim 1, wherein the tensioneradditionally comprises an offset member coupled with the shaft unit toconnect the peripheral unit with the shaft unit, the peripheral unitincludes a tension pulley and a bearing assembly mounted on the offsetmember to journal the tension pulley.
 14. The outboard motor as setforth in claim 13, wherein the tension pulley has a height taller than aheight of the bearing assembly.
 15. The outboard motor as set forth inclaim 1, wherein the tensioner additionally comprising a tensionadjuster to adjust a tensioning force of the tensioner.
 16. The outboardmotor as set forth in claim 15, wherein the tension adjuster includes abiasing member that biases the peripheral unit toward the flexibletransmitter relative to the engine body.
 17. The outboard motor as setforth in claim 1, wherein the damping mechanism has a damping axis alongwhich a shaft that is connected to the piston moves, the flexibletransmitter is moved in one direction by the first rotatable member, andthe damping axis is generally oriented toward a separating portion ofthe flexible transmitter where the transmitter is separating from theperipheral unit with the movement of the flexible transmitter in the onedirection.
 18. The outboard motor as set forth in claim 1, wherein theshaft unit is positioned at a second location which is capable to begenerally higher than the center axis of the peripheral unit when thedrive unit is tilted up about the tilt axis.
 19. The outboard motor asset forth in claim 1, wherein the flexible transmitter includes a beltor chain.
 20. An outboard motor comprising a drive unit, and a bracketassembly adapted to be mounted on an associated watercraft to supportthe drive unit for tilt movement about a horizontally extending tiltaxis, the drive unit comprising an internal combustion engine comprisingan engine body, a moveable member moveable relative to the engine body,the engine body and the moveable member together defining at least onecombustion chamber, a first rotatable member rotatable with the movementof the moveable member, an air intake system arranged to introduce airto the combustion chamber, the intake system comprising at least oneintake valve, an exhaust system arranged to route exhaust gases from thecombustion chamber, the exhaust system comprising at least one exhaustvalve, a valve actuation mechanism arranged to actuate at least one ofthe intake and exhaust valves between an open position and a closedposition, the valve actuation mechanism comprising a second rotatablemember arranged to engage the at least one of the intake and exhaustvalves, and a drive mechanism arranged on a top surface of the enginebody to drive the valve actuation mechanism, the drive mechanismcomprising a flexible transmitter to rotate the second rotatable memberwith the rotation of the first rotatable member, and a tensionerarranged to adjust tension of the flexible transmitter, the tensionercomprising a shaft unit mounted on the engine body, a peripheral unitswingably carried by the shaft unit and abutting on a portion of theflexible transmitter, a swing axis of the shaft unit being offset from acenter axis of the peripheral unit, and a damping mechanism to damp avibration of the flexible transmitter, the damping mechanism having adamping member that urges the peripheral unit toward the flexibletransmitter, and the damping member being positioned at a location whichis capable to be generally the highest of the damping mechanism when thedrive unit is tilted up about the tilt axis.
 21. The outboard motor asset forth in claim 20, wherein the damping mechanism additionallyincludes a hydraulic cylinder defining an internal cavity, a pistonslideably disposed within the internal cavity and defining first andsecond chambers on opposite sides thereof, the first and second chambersare filled with working fluid, the piston forms an orifice through whichthe first and second chambers communicate with each other, the dampingmember coupled with the piston and extending through the first chamberand beyond an end of the cylinder, a bias member disposed in the secondchamber to bias the piston such that the damping member extends outwardfrom the end.
 22. An outboard motor comprising a drive unit, and abracket assembly adapted to be mounted on an associated watercraft tosupport the drive unit for tilt movement about a horizontally extendingtilt axis, the drive unit comprising an internal combustion enginecomprising an engine body, a moveable member moveable relative to theengine body, a first rotatable member rotatable with the movement of themoveable member, an engine component actuation mechanism arranged toactuate at least one of engine components, the actuation mechanismcomprising a second rotatable member arranged to engage the enginecomponent, and a drive mechanism arranged on a top surface of the enginebody to drive the actuation mechanism, the drive mechanism comprising aflexible transmitter to rotate the second rotatable member with therotation of the first rotatable member, and a tensioner arranged toadjust tension of the flexible transmitter, the tensioner comprising ashaft unit mounted on the engine body, and a peripheral unit swingablycarried by the shaft unit and abutting on a portion of the flexibletransmitter, a swing axis of the shaft unit being offset from a centeraxis of the peripheral unit, and the shaft unit being positioned at alocation which is capable to be generally positioned higher than thecenter axis of the peripheral unit when the drive unit is tilted upabout the tilt axis.
 23. The outboard motor as set forth in claim 22,wherein the tensioner additionally comprises an offset member coupledwith the shaft unit to connect the peripheral unit with the shaft unit.